Organometallic compounds are used as a material for various purposes, such as transparent conductive oxide films for use in fabricating photovoltaic cells and flat panel displays. Many organometallic compounds, such as diethyl zinc (DEZn), easily decompose in the presence of trace moisture, trace oxygen, light, and in some cases heat. In doing so, the organometallic compounds generate metallic compounds. In the case of DEZn, decomposition produces solid Zn and ethane/ethylene which, due to the difference in vapor pressure between ethane/ethylene and DEZn, tends to accumulate in the vapor region and increase the pressure in the storage container. The metallic compound gradually deposits in the storage tank, the supply equipment parts, and the filling lines during storage, transportation, and supply of the organometallic compounds to a manufacturing tool. This becomes problematic because the metallic compound not only contaminates the manufacturing process, but also causes stoppage of parts used in the supply system. Further, the metallic compound may cause further deterioration of the organometallic compounds. In spite of the unstable properties of organometallic compounds, a strong demand remains in the semiconductor and photovoltaic industry to supply these unstable compounds to a manufacturing tool continuously while maintaining high purity.
As a result, purification techniques and supply techniques for organometallic compounds have been developed. JP Pat. No. H6-41151 discloses purification methods for diethyl zinc using column chromatography with activated carbon. JP Pat. No. 2002-3303391 discloses a method for removing impurities from trimethyl indium using sublimation. JP Pat. No. 2001-3217854 discloses a method for purifying a dry organometallic compound by contacting the dry organometallic compound with a copper or nickel catalyst to remove oxygen existing in the dry organometallic compound as an impurity.
However, even if such purification techniques are used, the purification techniques fail to address metallic impurities generated within tanks during storage, transportation, and supply. As a result, it is believed that no effective techniques addressing the stable supply of organometallic compounds have been disclosed to date. More specifically, simple and cost-effective techniques are needed to remove metal impurities generated in tanks and supply equipment during storage, transportation, and supply.
One standard transportation, storage, and supply technique for organometallic compounds is explained with reference to FIG. 1 and FIG. 2. FIG. 1 is a diagram of an exemplary prior art distribution route 100 for supplying organometallic compounds 110 from a production site 120 to a consumption plant 130. The production site 120 may be an overseas production site and the consumption plant 130 may be a domestic consumption plant. A transport tank 140 is filled with an organometallic compound 110 at the production site 120 where the organometallic compound 110 is produced. The transport tank 140 is then transported to a filling plant 150. The transport tank 140 may be transported to the filling plant 150 by a marine transport 160. At the filling plant 150, the organometallic compounds 110 are transferred from the transport tank 140 to one or more storage tanks 170a, 170b, and 170c. Each storage tank 170a, 170b, and 170c is transported to one or more consumers at various consumption plants 180a, 180b, and 180c. The one or more storage tanks 170a, 170b, and 170c may be transported to the consumption plants 180a, 180b, and 180c via a conveyance road.
One problem with the distribution route 100 is that, even if the organometallic compounds are highly purified prior to transport, the compounds will eventually decompose and generate decomposed metallic compounds. Some of these decomposed metallic compounds will diffuse in the organometallic compound and some of the compounds will deposit in the tank and supply equipment during storage and transport. Further, if the organometallic compounds in the transport tank are transported at elevated temperatures (e.g., 60° C.), the amount of decomposed metallic compounds will increase.
FIG. 2 is a diagram of a prior art method 200 for supplying organometallic compounds 110 from a supply tool 210 to a manufacturing tool 220. The storage tank 170 is connected to the supply tool 210 after the storage tank 170 is transported to the consumption plant. The organometallic compounds 110 in the storage tank 170 are then transferred to the supply tank, such as a bubbler 230. The organometallic compounds are then supplied to the manufacturing tool 220 using methods known in the art, for example, a bubbling supply method.
In order to transfer the liquid organometallic compound 110 from the storage tank 170 to the bubbler 230, a carrier gas 234 is introduced into the storage tank 170 through a carrier gas inlet line (not shown) and a carrier gas inlet valve 240 and the storage tank 170 is pressurized. When pressure in the storage tank 170 is increased, the liquid organometallic compound 110 is then transported through the siphon tube 250, and the compound is supplied to the bubbler 230 through a filling valve 260, a first supply pipe 270, a filter 280, and a filling valve 284 filling the bubbler 230 with the liquid organometallic compound 110. This filling system makes it possible to fill both an empty bubbler and a bubbler already containing the organometallic compound after the compound has been used and the volume of the compound in the bubbler decreases.
During supply to the manufacturing tool 220, a carrier gas 282 is introduced into the bubbler 230 through a carrier gas inlet valve 288 and sparger 286, and then the carrier gas 282 is dispersed in the liquid organometallic compound 224 in the bubbler 230. The carrier gas 282 introduced in the bubbler becomes saturated with the organometallic compound 224 and the saturated gas mixture is supplied to the manufacturing tool 220 through a supply valve 290 and a second supply pipe 294.
Deposits on the siphon tube 250, the filling valve 260, the first supply pipe 270, and the filter 280 of the metallic compounds generated due to decomposition of the organometallic compound in the storage tank 170 present several problems for the supply system, making it difficult to supply the organometallic compound to the manufacturing tool stably and continuously. The filter 280 may be easily clogged with the decomposed metallic compounds, requiring frequent repair and corresponding downtime of the supply system. The decomposed metallic compound is generated not only in the storage tank 170 but also in the bubbler 230. During bubbling supply, any decomposed metallic compound in the organometallic compound 224 in the bubbler 230 is scattered together with the gas mixture to the supply valve 290, the second supply pipe 294, and every device attached to the second supply pipe 294, for example, the mass flow controller, the mass flow meter, and any additional filters and valves (not shown in FIG. 2), which may clog these devices. Therefore it is difficult to supply an organometallic compound to a manufacturing tool stably and continuously.
Several techniques have been studied to solve the above problems caused by the decomposed metallic compounds. One technique attempts to reduce the decomposition of the organometallic compound by reducing moisture and oxygen on the surface of the tube and the tank, typically made of stainless steel. Moisture and oxygen are reduced by exposing the stainless steel surface to an electro polish and/or a high purity nitrogen purge process. However since some organometallic compounds only require heat to decompose, the electro polish and nitrogen purge to reduce moisture and oxygen are not a sufficient solution. This solution also takes time and personnel cost.
Another technique uses filtration to reduce the metallic compound. However removing moisture and oxygen on the filter remains difficult and the filters often become clogged with the metallic compound. Thus, these known techniques are not sufficient for reducing metallic compounds generated in organometallic compounds. Recently the demand for these organometallic compounds has increased, so a new solution for the stable supply of these compounds is highly desired by those in the semiconductor field and the photovoltaic field.